The integration of the day-ahead electricity markets in Europe shall lead to one multi-area market that will substitute the local/national ones. In view of the "target model" that will be enforced in all European markets in conjunction with their forthcoming coupling/integration, a centralized market splitting algorithm is implemented in this paper, respecting the standard market regulatory framework of power exchanges (PXs) and power pools, including 1) block offers/bids, linked block offers/bids, flexible hourly offers/bids and convertible block offers in power exchanges and 2) unit technical/commitment constraints and system operating constraints in power pools. The problem is formulated as a mixed integer linear programming (MILP) model, which can be solved using commercial MILP solvers. The performance and computational requirements of an implementation in pan-European level is presented in the companion paper; the model is tested in terms of problem solvability to its limits, considering a day-ahead market clearing time threshold equal to one hour.Index Terms-Internal electricity market, market splitting, mixed integer linear programming, power exchange, power pool.